These days, it is predominantly microlithographic projection exposure methods that are used for producing semiconductor components and other finely structured components, such as e.g. photolithography masks. In this case, use is made of masks (reticles) or other patterning devices that bear or form a pattern of a structure to be imaged, for example a line pattern of a layer of a semiconductor component. The pattern is positioned in the region of an object plane of the projection lens between an illumination system and a projection lens in a projection exposure apparatus and is illuminated by illumination radiation provided by the illumination system. The radiation modified by the pattern travels in the form of projection radiation through the projection lens, which images the pattern with a reduced scale onto the wafer to be exposed or onto the substrate to be exposed. The surface of the wafer is arranged in an image plane of the projection lens that is optically conjugate to the object plane. The wafer is generally coated with a radiation-sensitive layer (resist, photoresist).
One of the aims in the development of projection exposure apparatuses is to lithographically produce structures having smaller and smaller dimensions on the wafer. In the case of semiconductor components, for example, smaller structures lead to higher integration densities, which generally has a favourable effect on the performance of the microstructured components produced. Projection lenses exhibiting good imaging performance are desired for this purpose.
The small size of the structures to be imaged and the increasingly small size of the structures to be produced and the ultimate size and other limiting factors of the projection lens give rise to specific issues. By way of example, what are known as optical proximity effects can occur in the projection lens. In the structures produced, the effects can cause the produced structures to deviate in a typical manner from the associated forms of the structures to be imaged on the mask. For correcting optical proximity effects, DE 10 2007 021 649 A1 discloses an optical attenuation filter, which is designed in the form of a transmission filter for installation in the region of the pupil plane of a projection lens and exhibits a transmittance that varies as a function of the pupil spatial coordinate.